Vehicles produce soot (carbonaceous and metallic) particulate matter in a wide size range of 5 to 500 nanometer and more, mostly as exhaust fumes. Most of this, 90% in terms of mass, is above 300 nanometer and is filtered partially by vehicle exhausts and car air-conditioning systems on air intake to the vehicle cabin, but not all. In particular, so called nanoparticles in the size range 5 to 300 nanometer, which comprise the majority of the soot particles, 90% by number, are not filtered effectively. Such nanoparticles can be produced e.g., in South Los Angeles alone, at a rate of 13 tonnes per day by traffic.
Such nanoparticles, especially metallic ones, are now linked to a range of diseases, such as heart attacks, cancer, lung disease, and immune system diseases, and are considered a serious health problem. They pass rapidly (systemic in under 1 hour) into body cells, and are now considered a major trigger of heart attacks and other cardiovascular diseases.
Worse, they tend to accumulate within cars, school buses, lorry cabs and buildings close to main roads, typically four times but occasionally up to and over thirty times normal levels, so that road travelers and local residents are placed daily at high risk. Groups particularly seriously affected include professional drivers (trucks, taxis, buses, trams), ordinary commuters and schoolchildren (can have 50% of daily intake in a 30 minute commute), and those living and working within 400 meters of roads.
In 2000, the California Air Resources Board (CARB) estimated that diesel particulate material was responsible for 70 percent of the state's risk of cancer from airborne toxics in California, USA. In 2004 alone, diesel pollution will cause an estimated 3,000 premature deaths in California. In addition, diesel exhaust will cause an estimated 2,700 cases of chronic bronchitis and about 4,400 hospital admissions for cardiovascular and respiratory illnesses every year. The cost of these health impacts (in California alone) is $21.5 billion per year.
FIG. 1 shows ambient levels of nanoparticles encountered in different situations (for Switzerland). The ‘normal’ background level encountered, in an office, is curve 11, with a steady count (base, average and peak levels are all similar) of 2500 nanoparticle counts per cubic centimeter. On a road in woodland, curve 12 shows 6000 nanoparticle counts per cubic centimeter, again with base, average and peak levels all similar.
By contrast, curve 13 shows levels in a quiet village street, where the baseline count is much higher, about 12,000 nanoparticle counts per cubic centimeter, with an average around 20,000 nanoparticle counts per cubic centimeter, and peak values over 30,000 nanoparticle counts per cubic centimeter. Curve 14 shows levels at a motorway roadside (service station) near heavy traffic with ‘heavy fume’. The baseline count is about 15,000 nanoparticle counts per cubic centimeter, the average is about 30,000 nanoparticle counts per cubic centimeter (10 times ‘normal’), and the peak value is almost 70,000 nanoparticle counts per cubic centimeter. It should also be noted that after a high peak, recovery to the baseline is slow and takes well over a minute.
FIG. 2 shows similar measured values for the inside of a car (with continuous cabin air intake via the conventional filters of the air conditioning system) driving through a number of everyday situations. The measured peak values are, as expected, higher on the road than near to it, as In FIG. 1. The drive starts in a quiet quarter with little traffic (reference numeral 31) with about 10,000 nanoparticle counts per cubic centimeter. The two peaks 32 appear in the time period when the car was passing two tunnels: peak values of 175,000 and 250,000 nanoparticle counts per cubic centimeter (100 times normal). It can be seen that the relaxation curve portion 33 takes several minutes after having passed the tunnel to come down to the ‘low’ value of 30,000 nanoparticle counts per cubic centimeter (still 10 times normal). Reference number 34 is relate to a typical heavy motorway traffic/traffic jam situation, with peak levels, around 125,000 nanoparticle counts per cubic centimeter (50 times normal).
Measurements made simultaneously outside and inside the car, in situations where the car is completely closed, and the air conditioning on full recirculation mode via its conventional filters (so new air intake to the vehicle cabin is minimized—there is always some, both via the air conditioning system and via leaks), show that the best possible result achievable on such a drive, using such conventional measures to exclude nanoparticles, is to reduce the average nanoparticle count (for a complete journey) inside the car to about one-sixth (˜17%) of the average count experienced outside the car during the same journey.